The Optical Fiber Interferometric Sensors Based On Phase Modulation

This thesis researches various optical fiber interferometric temperature, relative humidity, refractive index and double parameters simultaneous measurement sensors based on phase modulation, and researches the solutions of temperature cross-sensitivity. Details are as follows:(1) The mode theory, the interference principles of multimode interference and fiber-optics interferometers, the working mechanisms of interferometric sensors, the theoretical basis and working principle of SD-OCT technology.(2) The sensors based on multimode interference:The first RI sensor is based on SMCS structure and its RI sensitivity is 170nm/RIU. The second high-sensitivity temperature sensor utilizes a RI-sensitive device's temperature cross-sensitivity property to enhance temperature sensitivity (up to 358pm/?), which is almost 30 times that of the inherent temperature sensitivity.(3) The sensing and imaging technology based on Michelson interferometer:The first sensor consists of a 3dB coupler and a section of Hi-Bi fiber spliced to one arm's end face of the coupler. It can be used for simultaneous monitoring of RI and temperature. The RI and temperature sensitivities are-30.1141dB/RIU and-1.057nm/?. The second sensor is constructed by splicing ?177?m PCF probe to one output port of a 3dB coupler with controllable offset. This sensor can sense temperature and RI information by two interference arms flexibly. Finally, the SD-OCT system based on Michelson interferometer and the OCT imaging research of colour paints, murals and jade samples were studied.(4) The RH sensors based on Fabry-Perot interferometer and PVA humidity-sensitive materials:The first sensor is constructed by splicing?105?m PCF to SMF and coating an ultrathin PVA film to the PCF's cleaved surface. The total length of this sensing head is only about 110?m This sensor can monitor the temperature and RH simultaneously. The second sensor is constructed by splicing ?100?m TCF (part of cladding is etched) to SMF and coated with PVA. The total length of this sensing probe is only about 105?m. This sensor can measure the ambient RH by demodulating the power variation of reflection spectrum. These two compact and flexible RH sensors have extensive applied range.(5) The temperature, RI and double parameters sensors based on MZI:The first sensor is constructed by splicing a section of DCF between two SMF and then cascading an FBG. FBG is insensitive to RI. It can monitor the temperature and RI simultaneously and the RI sensitivity is up to 232.8nm/RIU. The second sensor is a simple MMF-DCF-MMF structure, of which two short MMF play the roles of stimulating and recoupling cladding modes. Its temperature and RI sensitivities are 118pm/? and 66.32 nm/RIU. The third sensor has the ability of sensing temperature/strain or temperature/curvature at same time, which consists of input SMF, an FBG offset spliced with upstream input SMF, a short section of MMF and output SMF. The resonance wavelength of interference dip is used to monitor strain or curvature, and the Bragg peak is used to monitor temperature. The simultaneous measurement of double parameters can be realized through the demodulation matrixes. The fourth sensor consists of input SMF, HCF and output SMF, of which the HCF's inwall coating with a layer of ZnO film to improve the spectral pattern. Its temperature sensitivity is 25.24pnm/?.